PORE-SIZE DISTRIBUTION INDEX AS AN INDICATOR OF ATRAZINE MOVEMENT IN A CRETE SILT LOAM SOIL

Soil pore size distribution (PSD) may explain some of the variability in atrazine movement through soil. PSD and atrazine movement were correlated in an in situ study (field applied atrazine) and an in vitro study (laboratory applied atrazine). Undisturbed surface soil cores were taken from sprinkler-irrigated field plots on Crete silt loam (Pachic Argiustoll) under till and no-till corn (Zea mays L.) production. Soil cores were removed in June, July, August, and October 1989 for the in situ study and in November 1989 for the in vitro study. Water release data were collected from undisturbed cores using pressure plate apparatus, and the PSD index, lambda, was calculated. Atrazine concentrations were determined in the subsurface soil at 10 to 25-cm depth for the in situ study and in the water-release effluent for the in vitro study. Relative atrazine concentrations in the in situ July and August sub-surface samples were negatively correlated with lambda for June and July cores, respectively. For the in vitro study, the relative mass of atrazine in the water-release effluent was positively correlated with lambda. Different matric potentials, wetting and drying cycles, and amounts of applied water may explain differences between the in situ and the in vitro studies.